Written Findings of the State Noxious Weed Control Board - Class C Weed
Hoary Cress (Cardaria draba (L) Desv.) FamilyFamily: Brassicaceae (Cruciferae) Description and VariationDescription and Variation: Hoary cress is a perennial plant with a spreading root system from which many aerial shoots are produced. The stem is 30-60 cm, erect to occasionally nearly procumbent. The basal leaves are irregularly dentate to entire with scattered to dense pubescence. The middle and upper leaves are sparsely pubescent to glabrous, obovate, elliptic-oblong or lanceolate, irregularly toothed to nearly entire. The flowers are white and the seed pods are heart shaped. Economic ImportanceEconomic Importance: Detrimental - Cardaria draba is the most weedy of all three Cardaria species occurring in the United States. It has the potential to reduce the value of high-price wheat lands. Beneficial - The flowers of hoary cress serve as pollen and nectar sources for many insects. Geographical DistributionGeographical Distribution: Hoary cress is native to the Balkans, Georgia, Armenia, Azerbaijan, Irkutskaya Oblast, Turkey, Israel, Syria, Iraq, and Iran. It is widely introduced and is naturalized throughout Europe and all other continents. HabitatHabitat: Hoary cress is a significant hazard to crop production under moist conditions and on irrigated land, but is unlikely to be a problem in arid areas. C. draba shows a preference for alkaline soils, but does well on a variety of soils where moisture conditions are moderate. It grows under open, unshaded conditions in grain fields, hayfields, sugar beets, vegetable crops, and along roadsides. HistoryHistory: Hoary cress was first collected in the United States at Long Island, New York in 1862 and Ontario, Canada in 1878. It was probably introduced by early European settlers. Growth and DevelopmentGrowth and Development: The root system consists of vertical and lateral roots from which grow new rosettes and flowering shoots. It survives and spreads primarily by an extremely persistent root system. These overwintering roots give rise to new shoots in the spring. Studies indicate that the peak accumulation of carbohydrates is around the first of August with the lowest levels in early spring. Cotyledons appear about five to six weeks after planting and expand to maximum size in about three weeks. During this time, a rosette forms. After two to three more weeks, the lateral roots develop from the radicle. Lateral stem shoots appear after about 13-14 weeks. Inflorescences commonly do not form until after two years. The plants usually bloom in mid-June, with pod development being completed by the third week of July. A single plant established in the absence of competition has been reported to spread over an area 3.7 m in diameter during its first year of development. Other studies show radial increases of 61-76 cm annually. The plants are capable of producing up to 455 shoots in one year. ReproductionReproduction: Hoary cress is self-incompatible and is outcrossed by insects. One mature plant produces 1,200-4,800 seeds. One year old seed had an 84 percent germination rate. Two year old seed had a 31 percent germination rate and three year old seed did not germinate. Shoot development is from buds which can form on any part of the permanent root system. Shoots tend to occur most often at or just below the point where lateral roots bend down to become vertical. Such buds give rise directly to new rosettes if borne at or near the soil surface. Buds arising at deeper levels grow out as rhizomes. HybridsHybrids: Hoary cress is capable of hybridizing with C. chalepensis. Response to HerbicidesResponse to Herbicides: Please refer to the Pacific Northwest Weed Control Handbook that is updated annually. Read and follow current herbicide labels and recommendations for control. Response to Cultural MethodsResponse to Cultural Methods: Cultivation is the major factor in the spread of hoary cress in Australia. Studies in Canada have shown that it takes three consecutive years of intensive tillage to kill the root system. Studies have also shown that seeds are killed after being buried in moist, compacted manure for one month. ReferencesReferences: Grower's Weed ID Handbook. 1978. Hawkes, Whitson, Dennis. 1985. A Guide to Selected Weeds of Oregon Mulligan, G.A. and J.N. Findlay. 1974. The Biology of Canadian Weeds. 3. Cardaria draba, C. chalepensis and C. pubescens. Can. J. Plant Sci. 54:149-160 Miller, T.W. 1991. Hoary Cress and Related Whitetops. Extension Bulletin PNW 359. USDA-ARS. 1971. Common Weeds of the United States. Dover Publications, Inc., New York. |